The urinary system cleanses the blood and rids the body of excess water and waste in the form of urine. The urinary tract consists of two kidneys, two ureters (one from each kidney), tubes that drain urine from the kidneys into the bladder (a storage sac), and the urethra (the tube that transports the urine out of the body). Muscles help control the release of urine from the bladder.

The kidneys, a pair of bean-shaped organs, are located at the bottom of the ribcage in the right and left sides of the back. Although the body is equipped with two kidneys, you can function with one reasonably healthy kidney if the other is damaged or removed. The kidneys receive blood from the aorta, filter it, and send it back to the heart with the right balance of chemicals and fluid for use throughout the body. The urine created by the kidneys is moved out of the body via the urinary tract.

The kidneys control the quantity and quality of fluids within the body. They also produce hormones and vitamins that direct cell activities in many organs; the hormone renin, for example, helps control blood pressure. When the kidneys are not working properly, waste products and fluid can build up to dangerous levels, creating a life-threatening situation. Among the important substances the kidneys help to control are sodium, potassium, chloride, bicarbonate HCO3- (measured indirectly as CO2), pH, calcium, phosphate,

and magnesium.

Diseases and conditions affecting the kidney

In the US, kidney disease is the ninth leading cause of death; diabetes and high blood pressure are the most common causes of chronic kidney failure. (If you have diabetes or high blood pressure, you have a greater risk of developing kidney disease.

For links to more information, see the Related Pages Elsewhere on the Web below.) Any diseases that affect the blood vessels, including diabetes, high blood pressure, and atherosclerosis (hardening of the arteries), can impair the kidneys' ability to filter blood and regulate fluids in the body.

Disease and infection in other parts of the body can also trigger a kidney disorder. Because kidney impairment can be life-threatening, disorders and diseases that may affect the kidney deserve prompt attention.

Kidney disease often causes no symptoms until late in its course and can lead to end-stage kidney failure, which is fatal unless a dialysis machine is used or a kidney transplant is performed. There are more than 100 disorders, diseases, and conditions that can lead to progressive destruction of the kidneys. Some of the more common problems are described here. Warning signs that should not be ignored are also listed below.

Obstruction

The urinary tract can become blocked, or obstructed (for example, from a kidney stone, tumor, expanding uterus during pregnancy, or enlarged prostate gland). The buildup of urine can lead to infection and injury of the kidney. With a kidney stone, often the blockage is painful. Other obstructions may produce no symptoms and be detected only when a blood or urine test is abnormal or an imaging procedure, such as an x-ray or ultrasound, detects it.

Infection

Urinary tract infections, such as cystitis (an infection of the bladder), can lead to more serious infections further up the urinary tract. Symptoms include fever, frequent urination, sudden and urgent need to urinate, and pain or a burning feeling during urination.

There is often pressure or pain in the lower abdomen or back. Sometimes the urine has a strong or foul odor or is bloody. Pyelonephritis is an infection of kidney tissue; most often, it is the result of cystitis that has spread to the kidney.

An obstruction in the urinary tract can make a kidney infection more likely. Infections elsewhere in the body, including, for example, streptococcal infections, the skin infection impetigo, or a bacterial infection in the heart can also be carried through the bloodstream to the kidney and cause a problem there.

Glomerular diseases

Glomerular diseases are those that attack the blood filtering units of the kidneys. Diabetes and high blood pressure can lead to glomerular disease. Diseases of this type cause more cases of chronic kidney failure than any other cause.

The blood is continually filtered through microscopic clusters of looping blood vessels, called glomeruli. Attached to each glomerulus is a tiny tube (tubule) that collects the waste that has been filtered out. The filtering unit (glomerulus and tubule) is called a nephron.

Often, a glomerular disease is triggered by an abnormal reaction of the immune system. In this case, the body's own infection fighters mistakenly attack the kidney tissues. Sometimes, an autoimmune disorder such as systemic lupus erythematosus or Goodpasture syndrome is the cause.

The attack on the glomerulus may also be the result of an inherited condition. An attack on the glomerulus may also occur after a bacterial infection in another part of the body, such as a strep infection of the throat or skin, the skin infection impetigo, or an infection inside the heart.

Viruses, such as the HIV virus that leads to AIDS, can also trigger glomerular disease.

In diseases and conditions classified as glomerulonephritis (also called nephritis or nephritic syndrome), the glomeruli become inflamed.

As blood filtering becomes impaired, urine output decreases, water and waste products accumulate in the blood, and blood appears in the urine.

Because the blood cells break down, urine often becomes brown instead of red. Certain body tissues swell with the excess water (a condition called edema). Outcomes can vary: the condition may go away in a few weeks, permanently reduce kidney function, or progress to end-stage kidney failure.

In nephrotic syndrome, the blood loses protein to the urine because of damage to the membrane between the glomeruli and tubules. As the amount of albumin (a major protein) decreases in the blood, parts of the body swell with fluid (often around the eyes or in the belly or legs). Other diseases and illnesses may lead to this syndrome, and complications such as blood clots and high cholesterol may develop. Childhood nephrotic syndrome usually responds well to treatment and does not usually result in permanent kidney damage. .

Other factors

Any situation in which there is severe blood loss or reduced blood flow may prevent the kidneys from working correctly. Severe dehydration, some aortic and heart surgeries, a severe infection in the blood or heart, and severe heart failure are examples of events that can lead to sudden kidney problems.

The damage is usually reversible; although with shock or severe infection, the damage may be permanent. Some medications and diagnostic agents can have toxic effects. In some cases, nonsteroidal anti-inflammatories (NSAIDS, such as over-the-counter ibuprofen and various prescription drugs), x-ray dye, ACE inhibitors, and certain antibiotics can damage the kidneys. Acute (sudden) kidney failure may result, a condition that requires emergency medical treatment to prevent death.

Cancers involving the urinary system are not as common as those in other parts of the body. Kidney cancers are of two main types. One called Wilms tumor occurs in young children and is often detected as a firm swelling in the belly. Renal cell carcinoma, which occurs in middle-aged to older adults, can cause blood in the urine but is often not detected until it has spread to other parts of the body. Bladder cancers are more common, and often present with painless, bloody urine. In many cases, the blood is only detected when a urinalysis is performed. Because bladder cancers can be controlled when detected early, any urine bleeding in adults (except during a woman's menstrual period) should be checked by your doctor.

Signs and symptoms

Kidney disease often proceeds silently over many years, with no signs or symptoms the patient can recognize or with signs that are too general for the patient to suspect kidney trouble. For that reason, routine blood and urine tests are especially important; they detect blood or protein in the urine and abnormal chemical levels in the blood, such as creatinine and blood urea nitrogen (BUN), early signs of kidney disorder and failure. The following problems may, however, be warning signs of kidney disease and should not be ignored. Prompt medical attention is required when any of these conditions are present.

Swelling or puffiness, particularly around the eyes or in the face, wrists, abdomen, thighs or ankles

Urine that is foamy, bloody, or coffee-colored

A decrease in the amount of urine

Problems urinating, such as a burning feeling or abnormal discharge during urination, or a change in the frequency of urination, especially at night

Mid-back pain (flank), below the ribs, near where the kidneys are located

High blood pressure

Tests

Tests performed on samples of your blood and urine are the first line of defense in detecting kidney problems and minimizing damage. Tests of these types can show how well the kidneys are removing excess fluids and waste. When a structural problem is suspected, a variety of imaging tests can be used to evaluate the kidney. A sample of kidney tissue, a biopsy, is sometimes helpful in diagnosing the specific cause of the problem.

Tests commonly used for screening and diagnosis

There are several tests commonly used to help your health care provider recognize if you have kidney or urinary disease. A blood sample can be analyzed for creatinine (and estimated glomerular filtration rate (EGFR)) and blood urea nitrogen (BUN). The level of these waste products in the blood increases as kidney filtration declines.

Abnormal results are usually the first sign that kidney disease is present. A urine sample is typically also examined and analyzed (urinalysis) as part of routine screening.

This set of tests looks for indicators of kidney and urinary disease such as red blood cells, white blood cells (WBCs or leukocytes), and protein in the urine. If you have diabetes or high blood pressure, the amount of protein (microalbumin) in your urine should be checked at least yearly to detect kidney disease in its early stages. When you have symptoms suggesting infection, a urine culture can confirm the presence of a bacterial infection.

Tests to monitor kidney function

If you have been diagnosed with a kidney disease, your health care provider will order laboratory tests to help monitor kidney function. Blood levels of BUN and creatinine are measured from time to time to see if the kidney disease is getting worse.

The amount of calcium and phosphate in the blood and the balance of serum and urine electrolytes can also be measured, as these are often affected by kidney disease. Hemoglobin, measured as part of a complete blood count (CBC) may be measured (the kidneys make a hormone, erythropoietin, that controls red blood cell production).

Urine total protein can be used to test the effects of treatment in diabetes and nephrotic syndrome. Parathyroid hormone, which controls calcium levels, is often increased in kidney disease and is often checked to see if enough calcium and vitamin D are being taken to prevent bone damage.

Imaging techniques

If a structural problem or blockage is suspected, a picture of the kidneys can be helpful. Imaging techniques such as an ultrasound, CT scan (computed tomography), isotope scan, or intravenous pyelogram (IVP) may be used. Various x-ray procedures can also be employed, such as an intravenous urogram, micturating cystogram, or renal arteriogram (or angiogram).

Kidney biopsy

A biopsy can determine the cause of protein or blood in the urine and be used to monitor the effectiveness of treatment. Analyzing a small piece of kidney tissue can reveal the nature and extent of structural damage to a kidney. A biopsy, obtained using a biopsy needle and diagnostic imaging equipment, is often useful when disease of the glomerular filter is suspected.

Treatment

Treatment varies depending on the type of kidney or urinary disease present. In general, the earlier kidney or urinary disease is recognized, the more likely it is to be treatable.

Dietary restrictions, drug therapy, and surgical procedures may be appropriate. If the kidneys can no longer effectively remove waste and water from the body, a dialysis machine used several times a week can take over kidney filtration.

Kidney transplant surgery is another option when kidneys fail. If you have diabetes or high blood pressure, control of your blood pressure and blood sugar is extremely important to prevent or minimize kidney damage.

The author Farhana Islam who compiled the above piece resides in Canada.